The invention herein is directed toward the field of heat pump systems and particularly toward the field of charging techniques for the closed refrigerant loop of a heat pump system, especially one active in the cooling mode of operation.
Heat pump systems of many kinds are well known. One kind in common use employs indoor and outdoor coils connected by reversible expansion valves which operate in one direction during the heating mode of the heat pump system, and in the other direction during the cooling mode of operation. The heat pump systems typically additionally include a compressor to drive refrigerant through the respective coils one way or the other. Often the compressor itself is not reversible, so a four-way valve is employed to switch the compressor output from one coil to the other. A typical system further includes an accumulator at the input of the compressor, which generally acts to collect excess liquid refrigerant from refrigerant gas just before entry to the compressor.
As suggested, the compressor acts upon refrigerant gas. At the output of one of the coils, i.e. the condenser coil, the refrigerant will be in liquid phase because of the loss of heat from the refrigerant in the condenser. During the cooling mode of operation, the outdoor coil acts as the condensing coil.
It is thus addressed herein how best controllably to charge heat pump systems with refrigerant fluid during servicing in particular while the heat pump is in its cooling mode. More specifically, it is desired to prevent overcharging split system variable capacity heat pumps, in which one coil is outdoors and the other is indoors, during charging operation in the cooling operational mode of the heat pump system. Overcharging typically occurs in the field during charging operation by inexperienced field personnel conducting charging operation manually.
Once a heat pump is overcharged, liquid refrigerant may be injected into the compressor possibly causing it to fail. Additionally, complicated temperature and pressure corrections may have to be made as a result of overcharging, which require specialized equipment and consume inordinate amounts of time and other resources to perform.